Ever since Homo sapiens first wandered out of Africa, the story of humanity has been one of constant migration. Today, 213 million people in the world are living in a country other than the one in which they were born, according to U.N. statistics. Just ten countries absorb the majority of global migration, with the U.S. leading the pack by a wide margin.

The most important factor that determines a country's rate of immigration is the availability of jobs, Janne Batalova, an immigration policy analyst at the Migration Policy Institute, told Life's Little Mysteries. People who have moved to the U.S. account for 20 percent of the world's total migrants, according to a 2008 report from the U.N. Department of Economic and Social Affairs. Russia and Germany, two more countries with top 10 economies, follow behind the U.S. with about 5 percent of the world's migrants each.

"In terms of the U.S., it's widely known that no other countries can really match the economic, educational, and social mobility for people in all walks of life," Batalova said.

But while the economy is important, the openness of the society also determines how many immigrants enter a country. In Japan, xenophobic laws and traditions keep immigration numbers low, despite harboring the world's third largest economy, Batalova said.

Some Middle Eastern countries serve as exceptions to that rule, though, accepting large numbers of immigrants to work in the oil, service and construction industries while simultaneously maintaining closed societies.

For example, Saudi Arabia is the fourth most common destination for immigrants, with 3 percent of the world's migrants now living there, according to the U.N. report. Similarly, the Gulf States of Qatar, the United Arab Emirates and Kuwait now host more immigrants per capita than any other country in the world.

However, immigration in those Middle Eastern countries primarily involves workers coming to the country by themselves for a few years, and then returning home. When looking at people who arrive in a country, put down roots and stay for the rest of their lives, no other nation accepts nearly as many new citizens as the U.S., Batalova said.

This article has been updated to correct the total number of global migrants.